Cannot run external command once external terminal has been closed

If you close the terminal named `External` (which I believe is created by the plugin), then next commands won't be executed. It seems this terminal is created only on init thus the issue.

Reproduce the issue by closing the terminal named `External`, then attempting another external command. Inspect the extension's terminal initialization and command execution flow; done means commands still execute after that terminal has been closed, with behavior covered by a regression test if the project has a test setup.

Written by the indexing model from the issue text.